Method for separating actinides and lanthanides by liquid-liquid extraction using calixarenes

ABSTRACT

The invention involves a process for separating actinides and lanthanides by liquid-liquid extraction by means of calixarenes. 
     These calixarenes have the formula:                    
     with R 1  and R 2  being alkyl groups or o-nitrophenoxy alkyl groups and R 3  and R 4  being aryl groups, 
     and they are used in an organic liquid phase containing an organic diluent. The diluent and the calixarene concentration of the organic phase are chosen so as to ensure an enrichment of the organic phase with the actinide(s) and/or lanthanide(s) to be separated from an aqueous acid or saline solution.

FIELD OF THE INVENTION

This invention involves a process for separation of actinides andlanthanides from each other from an aqueous solution containing them.

Such solutions could be in particular aqueous solutions from usednuclear fuel treatment facilities, such as fuel dissolving solutions oraqueous effluents.

They could also be aqueous solutions from processing of rare earth,thorium and/or uranium ores.

More precisely, it involves separation of such metals by liquid-liquidextraction by means of calixarenes.

STATE OF THE PRIOR ART

Separation among lanthanides and actinides

In the former technique, liquid-liquid extraction processes were used toseparate lanthanides among themselves by means of organic extractorssuch as di(2-ethylhexyl)phosphoric acid, amines, quaternary ammoniumsalts and tributyl phosphate, as described in Engineering Techniques J6630-1 to J6630-8. The most selective extractor isdi(2-ethylhexyl)phosphoric acid, which favours extraction of heavylanthanides with low ionic radii.

Calixarenes substituted by acetamidophosphine oxide groups

The used of macrocyclic ligands such as calixarenes was also consideredfor extraction of actinides and lanthanides present in aqueous solutionsas described in document FR-A-2 729 958.

The calixarenes used in this document have the formula:

in which m is equal to 0 or 1, where

n is a whole number from 2 to 8, with 4·(m+1)×n·8

R¹ and R² which can be identical or different, are alkyl oro-nitrophenoxyalkyl groups, and

R³ and R⁴ which can identical or different, are alkyl or aryl groups.

These calixarenes can be used to extract actinides and lanthanides fromaqueous solutions from used nuclear fuel processing.

They are functionalised on their upper edges by acetamidophosphine oxidesubstituents which have good affinity for actinides and lanthanides andthey are substituted on the lower edge by alkyl or o-nitrophenoxyalkylgroups.

For liquid-liquid extraction of actinides and lanthanides, thesecalixarenes are dissolved in an appropriate organic diluent such asnitrophenyl alkyl ethers, such as orthonitrophenyl hexyl ether.

Good extraction rates are obtained with such an organic diluent, but itis impossible to separate the actinides and lanthanides from each other.

Document JP-A-06/228032 describes the use of a mixture of chloroform andanother organic solvent such as chlorobenzene or toluene to dissolve acalixarene in order to prepare calixarene films from the somutionobtained.

SUMMARY OF THE INVENTION

The invention precisely involves a process for separating actinides andlanthanides by means of such calixarenes, according to which the diluentand the calixarene concentration are chosen in order to obtain aseparation of the actinides and lanthanides from each other.

According to the invention, the process for separation of at least onemetal M1 chosen in the group of actinides and lanthanides from at leastone metal M2 chosen from the same group from an aqueous solutioncontaining M1 and M2, includes the following steps:

a) putting the aqueous solution of the aforesaid metals M1 and M2 intocontact with the organic liquid phase including

at least one calixarene with formula:

 in which:

R¹ and R² which can be identical or different, are alkyl oro-nitrophenoxyalkyl groups, and

R³ and R⁴ which can identical or different, are aryl groups; and

an organic diluent

the aforesaid diluent and the calixarene concentration of the organicphase being chosen so that the distribution coefficient of the metal(s)M1 between this organic phase and the aforesaid aqueous solution isgreater than 1 and the distribution coefficient of the metal(s) M2between this organic phase and the aforesaid aqueous solution is lessthan 1; and

b) separating the aforesaid aqueous solution from the aforesaid organicphase.

It should be remembered that the distribution coefficient of a metal Msuch as M1 or M2 is defined by the following formula:$D_{M} = \frac{\lbrack M\rbrack_{{org},{eq}}}{\lbrack M\rbrack_{{aq},{eq}}}$

in which [M]_(org,eq) corresponds to the concentration of the metal inthe organic phase at equilibrium, and [M]_(aq,eq) corresponds to theconcentration of this same metal in an aqueous solution at equilibrium.For example, the extraction can be monitored by a radioactive tracer.This distribution coefficient D is determined with respect to theactivity of the metal in the organic phase and the activity of the metalin the aqueous solution at equilibrium.

When D is greater than 1, the metal goes mostly into the organic phase;when D is less than 1, the metal remains mostly in the aqueous phase.

To separate various actinides and lanthanides by liquid-liquidextraction, the distribution coefficients of metals M1 to be extractedin the organic phase must be high with respect to those of metals M2which must remain in the aqueous phase.

According to the invention, it was found that by choosing an appropriateorganic diluent and by adjusting the calixarene concentration of theorganic phase, a coefficient D greater than 1 could be obtained forcertain elements and a coefficient D less than 1 for other elements,although this was practically impossible with the diluent used up untilnow, orthonitrophenyl alkyl ether.

The choice of diluent and calixarene concentration depend not just onthe metals to be separated but also on the nature of the startingaqueous solution, as will be seen below.

According to the invention, the choice of organic diluent can inparticular be made by determining the distribution coefficient D_(Gd) ofgadolinium between an organic phase composed of calixarene in solutionin the diluent and an aqueous solution of gadolinium. In this case, thediluents which are suitable are those for which the distributioncoefficient D_(Gd) of gadolinium between the organic phase and theaqueous solution of gadolinium is from 0.5 to 5 when the calixareneconcentration of the organic phase is from 10⁻⁴ to 10⁻³ mol/L.

Appropriate diluents could belong in particular to the group of heavyalcohols, for example with formula C_(n)H_(2n)O with n·7, particularlywith n from 7 to 13. Octanol and isotridecanol are examples of suchalcohols. Chlorinated solvents such as chloroform, dichloromethane and1,2-dichloroethane can also be used. Mixtures of diluents can also beused.

The calixarenes which can be used in the invention process are to beselected from those described in FR-A-2 729 958. Calixarenes whichcorrespond to formula (II) above must be used, and particularly those offormula (II) in which R¹ and R² are alkyl groups of 3 to 18 carbon atomsand R³ and R⁴ are phenyl groups.

The following formula can be given by way of example of calixareneswhich can be used:

in which Ph represents a phenyl group.

With the calixarenes used in the invention, the length of chain R¹ canvary because, as was seen, chain length has almost no influence on theextraction capacity of calixarene with respect to element of thelanthanide and actinide groups.

According to the invention, the calixarene concentration of the organicphase depends in particular on the organic diluent used. In general,calixarene concentrations are between 10⁻⁴ and 5·10⁻² mol/L.

The invention process can be used in the following manner.

First, the organic phase, which is immiscible in water, is prepared bydissolving calixarene in the diluent used, then the aqueous solutioncontaining the metals to be separated is mixed in and stirred for atleast 10 minutes at a temperature of 10° C. to 35° C. The two phases arethen separated by centrifuging of the mixture at a speed of at least2500 rotations/min, for example 3000 rotations/min, for about 5 minutes.

According to the invention, to improve the yield of extraction of themetal(s) M1 in the organic phase, the organic phase can be put incontact with the aqueous phase in several stages to enrich the organicphase with metal(s) M1 in each stage. After each contact, the organicliquid phase is separated from the aqueous solution. All of theoperations can be done in classic liquid-liquid extraction devices suchas mixer-settlers and centrifuge extractors.

After separation of the organic phase enriched with metal(s) M1, thesemetals can be retrieved in an aqueous re-extraction solution by puttingthe separated organic phase in contact with the aqueous re-extractionsolution, followed by separation of the organic phase and there-extraction solution. These operations can be done as before. Theaqueous re-extraction solution is preferably an aqueous solution of amineral acid with a pH·4.

Nitric acid solutions containing 10⁻⁴ to 10⁻¹ mol/L of nitric acid, andparticularly a 10⁻² mol/L nitric acid solution can be cited as anexample of an aqueous re-extraction solution.

The use of such an aqueous re-extraction solution is very advantageouswith respect to use of an aqueous solution containing a complexingagent, such as the aqueous re-extraction solutions used on FR-A-2 729958.

The aqueous re-extraction solution of the invention is non-complexing.It does not contain any organic compound such as the organic complexersused in FR-A-2 729 958 (methylene diphosphonic acid, oxalic acid, citricacid, oxalate or citrate); it has a very low mineral acid concentrationand it is also economical.

Other characteristics and advantages of the invention will be clearerwith a reading of the following description, given simply as anillustration and in no way limiting, with reference to the drawings inappendix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the changes in distribution coefficientsof rare earth metals as a function of their ionic radius, for twoaqueous starting solutions, three different organic diluents and acalixarene concentration A₅ ⁴ of 10⁻⁴ mol/L.

A₅ ⁴

FIG. 2 is a graph also illustrating the changes in distributioncoefficients of rare earth metals as a function of their ionic radius,for two aqueous starting solutions, three different organic diluents anda calixarene concentration A₅ ⁴ of 3·10⁻⁴ mol/L.

FIG. 3 is a graph illustrating the changes in distribution coefficientsof rare earth metals as a function of their ionic radius, for twoaqueous starting solutions, three different organic diluents and acalixarene concentration A₅ ⁴ of 10⁻⁴ mol/L.

FIG. 4 is a diagram illustrating the variations in distributioncoefficient D of La, Am, Pm, Sm, Eu, Gd, Tb, Ho, Er and Yb as a functionof the calixarene concentration A₅ ⁴ of the organic phase usingchloroform as the diluent.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In putting the invention process to use, an organic diluent andcalixarene concentration which will allow for separation betweenmetal(s) M1 and metal(s) M2 must be chosen.

For this purpose, the distribution coefficients of lanthanides andactinides are determined for the two following diluents:

chloroform, and

octanol

using various concentrations of calixarene in the organic phase, and anaqueous solution containing for example 10⁻⁶ mol/L and between 10⁻⁹ and3·10⁻² mol/L for elements which do not have stable isotopes, composedof:

either a saline medium containing 4 mol/L of NaNo₃ and 10⁻² mol/L ofNaNO₃,

or an acid medium of an aqueous solution containing 3 mol/L of nitricacid.

In order to determine these distribution coefficients D, 1.5 ml of theaqueous solution containing the metal and 1.5 ml of the organic liquidphase made from chloroform or octanol with a calixarene concentration of10⁻⁴, 3·10⁻³, or 10⁻³ mol/L are put into contact.

The solutions are put into contact in a 6 ml glass hemolysis tube withstirring at 25° C. After a half hour of contact, the two phases areseparated by centrifuging and the activity of each phase is determinedby liquid scintillation or by ·, · or · spectrometry.

The calixarene used is A₅ ⁴ calixarene according to formula (IV) givenabove.

FIG. 1 illustrates the results obtained for a calixarene A₅ ⁴concentration of 10⁻³ mol/L in chloroform or octanol. It also gives forcomparison the results obtained when the diluent is orthonitrophenylhexyl ether (NPHE) instead of chloroform or octanol.

This figure shows in the abscissa the rare earth elements in descendingorder of the ionic radii and in the ordinate the distributioncoefficients.

The points shown on this figure refer to the results obtained for theaqueous starting solution of saline medium, and for the aqueous startingsolution of acid medium (HNO₃, 3M).

These points are distinguished by the following symbols:

black triangle: saline medium, diluent CHCl₃,

white triangle: acid medium, diluent CHCl₃,

black square: saline medium, diluent octanol,

white square: acid medium, diluent octanol,

black circle: saline medium, diluent NPHE,

white circle: acid medium, diluent NPHE,

Given these results, it can be seen that the use of a diluent such aschloroform and octanol allows for separation of lanthanides when a 10⁻³mol/L concentration of calixarene is used. This separation is impossiblehowever with the diluent of the prior art, NPHE.

Thus, for a saline medium, metals M1 chosen from La, Am, Ce, Pr, Nd, Pm,Sm, Eu and Gd can be separated.

FIG. 2 illustrates the results obtained with the same diluents and thesame aqueous starting solutions when the A₅ ⁴ calixarene concentrationis 3·10⁻⁴ mol/L.

FIG. 2 also shows that a separation of lanthanides can be done,particularly when chloroform is used as the diluent with a calixareneconcentration is 3·10⁻⁴ mol/L.

FIG. 3 illustrates the results obtained with a A₅ ⁴ calixareneconcentration of 10⁻⁴ mol/L.

Examination of FIG. 3 shows that satisfactory lanthanide separation canbe obtained using octanol as a diluent.

It is also seen that, in the case of calixarenes, the lighter elementsof which the ionic radius is higher are better extracted, the contraryof the results with di(2-ethylhexyl)phosphoric acid used in the priorart which favours extraction of heavy elements with low ionic radii.

FIG. 4 shows variations of distribution coefficient D as a function ofthe A₅ ⁴ calixarene concentration for elements La, Am, Pm, Sm, Eu, Gd,Tb, Ho, Er and Yb extracted from a saline medium of the same compositionas before, using chloroform as the diluent.

Examination of this figure shows that numerous separations can be doneby appropriately choosing the calixarene concentration to have adistribution coefficient D greater than 1 for certain elements and adistribution coefficient D less than 1 for other elements.

Thus for a calixarene concentration of 10⁻³ mol/L, a very satisfactoryseparation of lanthanum and ytterbium can be done because thedistribution coefficient of lanthanum is in this case 140 while thedistribution coefficient of ytterbium is less than 0.19.

For separation of americium and europium, a A₅ ⁴ calixareneconcentration of 3·10⁻⁴ mol/L can be chosen for which D_(Am) is 3.47while D_(Eu) is 4.72·10⁻¹.

Examination of FIGS. 1 to 3 shows that, in the case of a saline startingmedium, metals M1 chosen from the group composed of trivalentlanthanides and actinides Am(III) and Cm (III) can be separated.

In this case, chloroform or octanol can be used as the diluent.

When the aqueous starting solution is an acid solution, metals M1 chosenfrom La, Ce, Pr, Nd, Pm, Sm and Eu can be separated, for example byusing chloroform and a calixarene concentration of 3·10⁻⁴ mol/L.

The invention process thus has numerous advantages with respect to theprior process described in FR-A-2 729 958 in which nitrophenyl alkylether was used as the diluent and a complexing solution forre-extraction.

Due to the choice of diluent, the calixarene concentration and aslightly acidic aqueous solution used for re-extraction, actinides andlanthanides can be separated from various aqueous media (acidic orsaline) without addition of disrupting organic compounds such ascomplexers.

The examples which follow illustrate separations done by the inventionprocess.

EXAMPLE 1

Separation of Lanthanum and Ytterbium

In this example, these two rare earth elements are separated from anaqueous solution made from a saline medium containing 4 mol/L of NaNO₃and 0.01 mol/L of HNO₃.

For this separation, an organic phase made from chloroform is usedcontaining 10⁻³ mol/L of calixarene A₅ ⁴.

FIG. 1 shows that this separation can be obtained with chloroform usingthis concentration. For this calixarene concentration, the distributioncoefficient of lanthanum is 140 while the distribution coefficient ofytterbium is 0.2

After extraction, the percentage of lanthanum extracted is equal to$\frac{D}{1 + D}*100$

99.9% lanthanum and 16.6% ytterbium are thus extracted in the organicphase. Re-extraction can then be done with 0.01 M nitric acid.

EXAMPLE 2

Separation of Lanthanum and Ytterbium

In this example, the same approach as in example 1 is used, but theorganic phase is made from chloroform containing 3·10⁻⁴ mol/L of thesame calixarene.

Examination of FIG. 2 shows that in these conditions, the distributioncoefficient of lanthanum is equal to 15 while the distributioncoefficient of ytterbium is 0.02.

93.8% lanthanum and 2% ytterbium is thus extracted.

As before, the re-extraction can be done with 10⁻² M nitric acid, thusbringing the composition of the aqueous solution from 50-50% lanthanumand ytterbium to 93% lanthanum and 2% ytterbium.

EXAMPLE 3

Separation of Europium and Gadolinium

In this example, the starting solution is an aqueous solution made froma saline medium with 4 mol/L of NaNO₃ and 0.01 mol/L of HNO₃.

Referring to FIG. 4, it is seen that the europium/gadolinium separationcan be done using as diluent chloroform and a A₅ ⁴ calixareneconcentration of 4.6·10⁻⁴ mol/L. In these conditions, the distributioncoefficient of europium is 1.12 and the distribution coefficient ofgadolinium is 0.88. The percentage of europium extracted is thus 52.8%and the percentage of gadolinium extracted is 46.8%. With re-extractionusing 0.01 N nitric acid and the aqueous solution undergoingre-extraction (after having added 4 mol/L of NaNO₃) an extraction by thesame organic phase, then repeating these operations several times, anenrichment of the organic phase in europium is obtained and a goodseparation.

EXAMPLE 4

Separation of Europium

In this example, the influence of europium and calixarene concentrationon the separation of europium from an acid medium (HNO₃ 3 M) and/or asaline medium (NaNO₃ 4M, HNO₃ 0.01 M) is studied. The extraction is doneby putting 2 ml of the aqueous solution containing 10⁻⁶ or 10⁻⁴ mol/L ofeuropium with 2 ml of the organic phases composed of A₃ ⁴ calixarene offormula (III) dissolved in chloroform in a concentration of 10⁻³ or 10⁻²mol/L. The activities of europium in the two phases are determined bycounting on 0.5 ml of the organic phase and 1 ml of the aqueous phase tocalculate the distribution coefficient D. 1.25 ml of the organic phasethen undergoes re-extraction with 2.5 ml of the aqueous re-extractionsolution composed of 0.01 M nitric acid. After re-extraction, theeuropium activities are determined on 0.2 ml of the organic phase and 1ml of the aqueous phase. The coefficient D for the re-extraction ofeuropium is also determined.

The results obtained are given in table 1 which follows for twoconcentrations of A₃ ⁴ calixarene and two concentrations of europium.

These results show that there are good rates of extraction andre-extraction of europium.

EXAMPLE 5

Separation of Europium

In this example, the influence of the europium concentration, thecalixarene concentration and the nature of the starting solution (acidor saline medium) on the extraction of europium are also studied usingas calixarene A₅ ⁴of formula (IV) in chloroform, a 0.01 M nitric acidsolution for re-extraction and an acid medium or saline medium of thesame composition as in example 4.

The following approach is used.

For extraction, 2 ml of the aqueous solution is put in contact with 2 mlof the organic phase, then the activity of europium is determined bycounting on 0.5 ml of the organic phase and 1 ml of the aqueous phase.The re-extraction is done with a double volume of aqueous solution bybringing into contact 1.25 ml of the preceding organic phase with 2.5 mlof the aqueous re-extraction solution, and the activity of europium isdetermined by counting on 1 ml of organic phase and 1 ml of aqueoussolution.

The results obtained with two concentrations of A₅ ⁴ calixarene, twoconcentrations of europium and an acid or saline starting medium aregiven in table 2.

EXAMPLE 6

Separation of Europium

In this example, the influence of the europium concentration and thecalixarene concentration on europium extraction is studied from an acidmedium or saline medium of the same composition as in example 4 using ascalixarene A₁₂ ⁴ calixarene of formula (IV).

The same procedure as in example 5 is used except that the re-extractionis done volume to volume using 1.25 ml of organic phase and 1.25 ml ofaqueous re-extraction solution.

The results obtained are given in table 3.

EXAMPLE 7

Separation of Europium

In this example, europium is extracted from an aqueous acid or salinesolution with the same composition as those given in example 4, using asthe organic phase A₁₂ ⁴ calixarene of formula (V) in a concentration of10⁻³ mol/L or 10⁻² mol/L in 1-octanol.

The extraction is done by putting 1.5 ml of the aqueous solution incontact with 1.5 ml of the liquid organic phase and the activity ofeuropium is determined by counting on 1 ml of the organic phase and 1 mlof the aqueous phase. Re-extraction of the extracted europium is thendone in the organic phase by putting into contact 0.8 ml of the organicphase with 0.8 ml of 0.01 M nitric acid. The activity of the organic andaqueous phases are then determined by counting on 0.5 ml of phase ineach case.

The results obtained are given in table 4. These results show that there-extraction is good when the extraction was done from an acid mediumand fairly good in the case of saline medium as long as the calixareneconcentration is low.

EXAMPLE 8

Separation of Americium

In this example, the liquid extraction phase of 1-octanol containing 10mol/L or 10 mol/L A₁₂ ⁴ calixarene. The aqueous phase is composed of anacid solution or saline medium of the same composition as that of thepreceding examples containing 2·10⁻⁹ mol/L of americium.

The extraction is done by bringing 1.5 ml of the aqueous solution intocontact with 1.5 ml of the organic phase, then the activity of americiumis determined on 100 μl of each phase in 14.9 ml of scintillatingliquid. The re-extraction of americium is done by putting 1.25 ml of theorganic phase into contact with 2.5 ml of the 0.01 M nitric acidsolution and the activity of the two phases is determined afterre-extraction on 100 μl of each phase in 14.9 ml of scintillatingliquid.

The results obtained are given in table 5.

EXAMPLE 9

Separation of Curium

The same approach as in the preceding examples is used to separatecurium from an aqueous acid or saline solution using the same organicphase and the same re-extraction solution.

The results obtained are given in table 6.

EXAMPLE 10

Separation of europium

In this example, europium is separated from an aqueous acid solution (3Mnitric acid) or saline solution (4M sodium nitrate) using an organicliquid phase composed of A₁₂ ⁴ calixarene in a concentration of 10⁻²mol/L in isotridecanol. In order to dissolve the calixarene in thisorganic phase, it is first dissolved in a mixture of chloroform andisotridecanol, then the chloroform is evaporated. The extraction andre-extraction are done in the same conditions as those in example 7.

The results obtained are given in table 7.

It is seen that the extraction is excellent for both media and that there-extraction is better in the case of saline medium.

EXAMPLE 11

Separation of Lanthanum, Samarium, Gadolinium, Holmium, Erbium andAmericium.

A liquid organic phase for carrying out this separation can be chosen byreferring to FIG. 4 which shows that to extract lanthanumpreferentially, a calixarene concentration of 1.41·10⁻⁴ mol/L inchloroform should be used. In this case, the distribution coefficientsof the elements are the following:

D_(La)=1.7

D_(Sm)=0.21

D_(Gd)=0.14

D_(Ho)=0.02

D_(Er)=0.02, and

D_(Am)=0.84

The percentage of the metals extracted are thus:

63% lanthanum

17% samarium

12% gadolinium

2% holmium

1.9% erbium and

45% americium

The processing of the organic phase can be continued by doing are-extraction and then several new extraction-re-extraction cyclesseveral times to selectively separate lanthanum from the other metals.

Americium is then separated using a 3·10⁻⁴ mol/L concentration ofcalixarene in chloroform. In these conditions, the distributioncoefficients of the various elements are as follows:

D_(Sm)=0.8

D_(Gd)=0.4

D_(Ho)=0.06

D_(Er)=0.05, and

D_(Am)=3.5

By thus doing the extraction, the following can be extracted:

78% americium

44% samarium

28.5% gadolinium

6% holmium

5% erbium

This allows for selective extraction of the americium and its separationfrom the solution after several extraction-re-extraction cycles.

TABLE 1 Concent. of A₃ ⁴ Concent. Dre- % re- extract. of Eu Medium Dext.ext. % ext. ext. 10⁻³ M 10⁻⁶ M acid 19.3 6.37 · 95.1 99.9 10⁻⁴ ″ 10⁻⁴ Macid 11.9 5.78 · 92.2 99.9 10⁻⁴ 10⁻² M 10⁻⁶ M acid 838 4.90 · 99.9 99.510⁻³ ″ 10⁻⁴ M acid 1.08 · 2.70 · 99.9 99.7 10³ 10⁻³ 10⁻³ M 10⁻⁶ M saline4.11 1.82 · 80.5 99.8 10⁻³ ″ 10⁻⁴ M saline 3.93 4.70 · 79.7 99.9 10⁻⁴10⁻² M 10⁻⁶ M saline 6.43 · 3.24 · 99.8 99.7 10² 10⁻³ ″ 10⁻⁴ M saline5.94 · 1.23 · 99.8 99.9 10⁻² 10⁻³

TABLE 2 Concent. of A₅ ⁴ Concent. Dre- % re- Extract of Eu Medium Dext.ext. % ext. ext. 10⁻³ M 10⁻⁶ M acid 16.61 2.10 · 94.3 99.8 10⁻³ ″ 10⁻⁴ Macid 10.8 7.38 · 91.5 99.9 10⁻⁴ 10⁻² M 10⁻⁶ M acid 6.53 · 9.4 · 99.999.1 10² 10⁻³ ″ 10⁻⁴ M acid 9.27 · 5.48 · 99.9 99.5 10² 10⁻³ 10⁻³ M 10⁻⁶M saline 3.40 2.31 · 77.3 99.8 10⁻³ ″ 10⁻⁴ M saline 3.27 — 76.6 — 10⁻² M10⁻⁶ M saline 4.77 · 5.78 · 99.8 99.4 10² 10⁻³ ″ 10⁻⁴ M saline 6.01 ·3.96 · 99.8 99.6 10² 10⁻³

TABLE 3 Concent. of A₁₂ ⁴ Concent. Dre- % re- extract. of Eu MediumDext. ext. % ext. ext. 10⁻³ M 10⁻⁶ M acid 22.9 4.17 · 95.8 99.6 10⁻³ ″10⁻⁴ M acid 15.1 9.30 · 93.8 99.9 10⁻⁴ 10⁻² M 10⁻⁶ M acid 1.46 · — 99.9— 10³ ″ 10⁻⁴ M acid 1.18 · 1.25 · 99.9 98.8 10³ 10⁻² 10⁻³ M 10⁻⁶ Msaline 4.90 3.80 · 83.0 99.6 10⁻³ ″ 10⁻⁴ M saline 3.84 9.41 · 79.3 99.910⁻⁴ 10⁻² M 10⁻⁶ M saline 5.36 · 2.10 · 99.8 97.9 10² 10⁻² ″ 10⁻⁴ Msaline 7.37 · 6.75 · 99.9 99.3 10² 10⁻³

TABLE 4 Concent. of A₁₂ ⁴ % re- extract. Medium Dext. Dre-ext. % ext.ext. 10⁻³ M saline 80.8 8.2 · 98.8 99.2 10⁻³ 10⁻² M saline 1440 0.2199.9 82.2 10⁻³ M acid 0.51 0.20 33.8 83.1 10⁻² M acid 2.53 6.7 96.2 13.0

TABLE 5 Concent. of A₁₂ ⁴ % re- extract. Medium Dext. Dre-ext. % ext.ext. 10⁻³ M acid 2.4 1.4 70.5 42.3 10⁻² M acid 170 7.6 99.4 1.3 10⁻³ Msaline 70 0.018 98.6 98.3 10⁻² M saline 2800 1.14 99.9 46.8

TABLE 6 Concent. of A₁₂ ⁴ % re- extract. Medium Dext. Dre-ext. % ext.ext. 10⁻³ M acid    1 0.55 50.1 64.6 10⁻² M acid   70 32.5 98.6 3.0 10⁻³M saline   280 0.011 99.6 98.9 10⁻² M saline 1 050 0.49 99.9 67.2

TABLE 7 Concent. of A₁₂ ⁴ % re- extract. Medium Dext. Dre-ext. % ext.ext. 10⁻² M acid 128 9.5 99.2 9.5 10⁻² M saline 2300 0.075 99.9 93.0

What is claimed is:
 1. A process for separating at least one metal M1selected from the group consisting of actinides and lanthanides from atleast one other metal M2 selected from the group consisting of actinidesand lanides from an aqueous solution containing M1 and M2, comprising:(a) contacting said aqueous solution containing M1 and M2 with anorganic liquid phase comprising (i) at least one caliene of the formula:

 wherein R¹ and R², which can be the same or different, are alkyl oro-nitophenoxyalkyl groups, and R³ and R⁴, which can be the same ordifferent, are aryl groups; and (ii) an organic diluent selected fromtho group consisting of the heavy alcohols and chlorinated solvents,wherein said organic diluent and the calixarene concentration are suchthat the distribution coefficient of the metal(s) M1 between saidorganic liquid phase and said aqueous solution is greater than 1 and thedistribution coefficient of the metal(s) M2 between said organic liquidphase and said aqueous solution is less than 1; and (b) separating saidaqueous solution from said organic liquid phase.
 2. The processaccording to claim 1, wherein said organic diluent is such that for acalixarene concentration in the organic phase of 10⁻⁴ to 10⁻³ mol/L, thedistribution coefficient of gadolinium between said organic phase and anaqueous solution of gadolinium is from 0.5 to
 5. 3. The processaccording to claim 1, wherein said organic diluent is chloroform oroctanol.
 4. The process according to claim 3, wherein said organicdiluent is chloroform or octanol.
 5. The process according to claim 1,wherein the concentration of calixarene(s) in said organic phase is 10⁻⁴mol/L to 5·10⁻² mol/L.
 6. The process according to claim 1, wherein R¹and R² are alkyl groups of 3 to 18 carbon atoms and R³ and R⁴ representthe phenyl group.
 7. The process according to claim 1, furthercomprising: (c) re-extracting the metals extracted into said organicliquid phase by contacting said organic liquid phase separated in (b)with an aqueous solution of a mineral acid having a pH less than orequal to
 4. 8. The process according to claim 7, wherein said aqueoussolution of a mineral acid is a nitric acid solution with a nitric acidconcentration of 10⁻⁴ to 10⁻¹ mol/L.
 9. The process according to claim1, wherein said aqueous solution is a saline solution, and the metals M1are selected from the group consisting of trivalent lanthanides, Am(III)and Cm(III).
 10. The process according to claim 9, wherein said organicdiluent is chloroform or octanol.
 11. The process according to claim 1,wherein said aqueous solution is acidic, and the metal(s) M1 areselected from the group consisting of La, Ce, Pr, Nd, Pm, Sm and Eu. 12.The process according to claim 11, wherein said organic diluent ischloroform and the calixarene concentration is 3·10⁻⁴ mol/L.
 13. Theprocess according to claim 1, wherein M1 is americium, M2 is europium,said aqueous solution is a saline solution, said organic diluent ischloroform, and the calixarene concentration is 3·10⁻⁴ mol/L.